Causes of Depression
How Is Biology Related to Depression?
Researchers have noted differences in the brains of people who have a clinical depression as compared to those who do not. For instance, the hippocampus, a small part of the brain that is vital to the storage of memories, appears to be smaller in some people with a history of depression than in those who've never been depressed. A smaller hippocampus has fewer serotonin receptors. Serotonin is one of many brain chemicals known as neurotransmitters that allow communication across circuits that connect different brain regions involved in processing emotions.
Scientists do not know why the hippocampus may be smaller in some people with depression. Some researchers have found that the stress hormone cortisol is produced in excess in depressed people. These investigators believe that cortisol has a toxic or "shrinking" effect on the development of hippocampus. Some experts theorize that depressed people are simply born with a smaller hippocampus and are therefore inclined to suffer from depression. There are many other brain regions, and pathways between specific regions, thought to be involved with depression, and likely, no single brain structure or pathway fully accounts for clinical depression.
One thing is certain -- depression is a complex illness with many contributing factors. The latest scans and studies of brain structure and function suggest that antidepressants can exert what are called "neurotrophic effects," meaning that they can help sustain nerve cells, prevent them from dying, and allow them to form stronger connections that withstand biological stresses. As scientists gain a better understanding of the causes of depression, health professionals will be able to make better "tailored" diagnoses and, in turn, prescribe more effective treatment plans.
How Is Genetics Linked to the Risk of Depression?
We know that depression can sometimes run in families. This suggests that there's at least a partial genetic link to depression. Children, siblings, and parents of people with severe depression are somewhat more likely to suffer from depression than are members of the general population. Multiple genes interacting with one another in special ways probably contribute to the various types of depression that run in families. Yet despite the evidence of a family link to depression, it is unlikely that there is a single "depression" gene, but rather, many genes that each contribute small effects toward depression when they interact with the environment.